The present inventive concept relates to a tap changer and, more particularly, to a tap changer in which movable contacts rotate to be selectively connected to a plurality of taps.
In general, a tap changer is installed in the primary windings of transformers in order to prevent iron cores from being supersaturated when a voltage level of a primary side of the transformer increases to an overvoltage level, equal to or higher than that of a rated voltage.
When a voltage of a secondary side is changed from a rated voltage having a predetermined level due to a change in a voltage level of the primary side, the tap changer serves to adjust the level of the voltage of the secondary side to be equal to that of the rated voltage.
FIGS. 1 through 5 are perspective views and circuit diagrams of a movable contact and a fixed contact illustrating a tap changing operation of a prior art tap changer.
Specifically, FIG. 1 illustrates a case in which tap {circle around (e)} and tap {circle around (f)} are connected, FIG. 2 illustrates a case in which tap {circle around (d)} and tap {circle around (f)} are connected, FIG. 3 illustrates a case in which tap {circle around (d)} and tap {circle around (g)} are connected, FIG. 4 illustrates a case in which tap {circle around (c)} and tap {circle around (g)} are connected, and FIG. 5 illustrates a case in which tap {circle around (c)} and tap {circle around (h)} are connected.
Referring to FIGS. 1 through 5, the prior art tap changer includes an upper movable contact 10 and a lower movable contact 20 coupled to a rotational shaft 40, and a plurality of fixed contacts 30c to 30h disposed in rotation tracks of the upper movable contact 10 and the lower movable contact 20.
The upper movable contact 10 includes a frame 11 rotatably coupled to the rotational shaft 40 and connection conductors 12 coupled to the frame 11 and selectively connected to the plurality of fixed contacts 30c to 30h according to rotation of the frame 11.
Like the upper movable contact 10, the lower movable contact 20 includes a frame 21 rotatably coupled to the rotational shaft 40 and connection conductors 22 coupled to the frame 21 and selectively connected to the plurality of fixed contacts 30c to 30h according to rotation of the frame 21.
Here, the upper movable contact 10 and the lower movable contact 20 are electrically connected to each other.
The frame 11 of the upper movable contact 10 includes a power transmission unit 13 to which an operating unit (not shown) for rotating the upper movable contact 10 is connected. Here, the operating unit pushes the power transmission unit 13 to rotate the upper movable contact 10.
The frame 21 of the lower movable contact 20 includes a power transmission unit 23 to which an operating unit (not shown) for rotating lower movable contact 20 is connected. Here, the operating unit pushes the power transmission unit 23 to rotate the lower movable contact 20.
A first fixed contact 30c, a second fixed contact 30d, and a third fixed contact 30e are disposed in the rotation track of the upper movable contact 10.
A fourth fixed contact 30f, a fifth fixed contact 30g, and a sixth fixed contact 30h are disposed in the rotation track of the lower movable contact 20.
Referring to the circuit diagrams of FIGS. 1 through 5, tap {circle around (a)} corresponds to a minimum number of turns of a coil, and a final number of turns of the coil is determined in tap {circle around (b)} as any one of tap {circle around (c)}, tap {circle around (d)}, and tap {circle around (e)} and any one of tap {circle around (c)}, tap {circle around (d)}, and tap {circle around (e)} are connected by the movable contacts.
Here, tap {circle around (c)}, tap {circle around (d)}, tap {circle around (e)}, tap {circle around (f)}, tap {circle around (g)}, and tap {circle around (h)} may be set to have predetermined differences in number of turns.
For example, in a case in which a minimum number of turns to tap {circle around (a)} is 90 turns, when tap {circle around (a)} and tap {circle around (b)} are directly connected, the number of turns of the coil is 90 turns.
Also, in a case in which a reference number of turns is 10 turns, when tap {circle around (e)} and tap {circle around (f)} are connected, since a difference in the number of turns of tap {circle around (e)} and tap {circle around (f)} is 10 turns, 10 turns are added between tap {circle around (a)} and tap {circle around (b)}, and thus, the final number of turns is 100 turns (90 turns+10 turns).
Also, when tap {circle around (d)} and tap {circle around (f)} are connected, since a difference in number of turns between tap {circle around (d)} and tap {circle around (f)} is 20 turns, 20 turns are added between tap {circle around (a)} and tap {circle around (b)}, and thus, a final number of turns of the coil is 110 turns (90 turns+20 turns).
Under the same principle, when tap {circle around (c)} and tap {circle around (h)} are connected, since a difference in number of turns between tap {circle around (c)} and tap {circle around (h)} is 50 turns, 50 turns are added between tap {circle around (a)} and tap {circle around (b)}, and thus, a final number of turns of the coil is 140 turns (90 turns+50 turns).
Hereinafter, a tap changing operation of the tap changer according to the prior art will be described with reference to FIGS. 1 through 5.
Referring to FIGS. 1 through 5, the first fixed contact 30c, the second fixed contact 30d, and the third fixed contact 30e are disposed in the rotation track of the upper movable contact 10, and the fourth fixed contact 30f, the fifth fixed contact 30g, and the sixth fixed contact 30h are disposed in the rotation track of the lower movable contact 20.
Here, the first fixed contact 30c is connected to tap {circle around (c)}, the second fixed contact 30d is connected to tap {circle around (d)}, the third fixed contact 30e is connected to tap {circle around (e)}, the fourth fixed contact 30f is connected to tap {circle around (f)}, the fifth fixed contact 30g is connected to tap {circle around (g)}, and the sixth fixed contact 30h is connected to tap {circle around (h)}.
First, FIG. 1 illustrates a case in which tap {circle around (e)} and tap {circle around (f)} are connected. The upper movable contact 10 is connected to the third fixed contact 30e, and the lower movable contact 20 is connected to the fourth fixed contact 30f. 
FIG. 2 illustrates a case in which tap {circle around (d)} and tap {circle around (f)} are connected. Here, the upper movable contact 10 rotates in one direction so as to be connected to the second fixed contact 30d, and the lower movable contact 20 is connected to the fourth fixed contact 30f. 
FIG. 3 illustrates a case in which tap {circle around (d)} and tap {circle around (g)} are connected. Here, the upper movable contact 10 is connected to the second fixed contact 30d and the lower movable contact 20 rotates in one direction so as to be connected to the fifth fixed contact 30g. 
FIG. 4 illustrates a case in which tap {circle around (c)} and tap {circle around (g)} are connected. Here, the upper movable contact 10 rotates in one direction so as to be connected to the first fixed contact 30c and the lower movable contact 20 is connected to the fifth fixed contact 30g. 
FIG. 5 illustrates a case in which tap {circle around (c)} and tap {circle around (h)} are connected. Here, the upper movable contact 10 is connected to the first fixed contact 30c and the lower movable contact 20 rotates in one direction so as to be connected to the sixth fixed contact 30h. 
However, in the prior art tap changer, since the upper movable contact 10 and the lower movable contact 20 are independently driven, an operating unit (not shown) for operating the upper movable contact 10 and an operating unit (not shown) for operating the lower movable contact 20 need to be separately provided, resulting in an increase in the number of components of the device, an increase in the volume of the device, and the necessity to control the plurality of operating units.